This invention relates to a thin magnetic metal film type magnetic recording medium comprising a thin magnetic metal layer as a magnetic layer on a non-magnetic substrate,
In the field of video tape recorders, for example, there is a stronger demand for high density recording with a view to achieving high picture quality. As a magnetic recording medium for accommodating such demand, a so-called thin magnetic film type magnetic recording medium has been proposed, in which a magnetic layer is formed on the non-magnetic substrate by directly depositing a magnetic material of metal or a Co--Ni alloy on the substrate by plating or vacuum thin film forming techniques, such as vacuum deposition, sputtering or ion plating.
The magnetic recording medium of the thin magnetic film type has many advantages, including superior coercivity, rectangular ratio and electro-magnetic conversion characteristics in the short wavelength range, only little demagnetization during recording, only little thickness loss during reproduction because of the reduced thickness of the recording layer and high packing density of the magnetic material because it is unnecessary to mix the non-magnetic binder material into the magnetic layer.
In such magnetic recording medium, attempts have been made to increase the track density and the recording density of the magnetic recording medium in order to accommodate the increased recording density. However, if the recording density becomes higher, spacing losses are increased. Consequently, a smooth surface of the magnetic recording medium tends to be preferred in order to prevent the adverse effects of the increased spacing losses.
However, if the surface of the magnetic recording medium is smoothed excessively, the magnetic head tends to be adsorbed onto the recording medium, so that the force of friction therebetween is increased, with the result that the recording medium is injured by a larger shearing force generated therein.
In order to assure satisfactory still characteristics, it has been practiced to provide surface protrusions on the non-magnetic substrate and thereby to afford moderate roughness to the surface of the magnetic layer or the protective layer stacked on the non-magnetic recording medium so as to control surface properties of the magnetic recording medium.
For controlling the surface properties of the magnetic recording medium as described above, the size control of the surface protrusions formed on the non-magnetic recording medium becomes crucial. That is, the larger the size of the surface protrusions, the more pronounced becomes the problem of the spacing loss, with the result that the electro-magnetic conversion characteristics are deteriorated. Conversely, should the surface protrusions be restricted in height, a sufficient running durability cannot be maintained, although the adverse effects of the spacing losses may be eliminated.
Thus it is believed to be extremely difficult to control the size as well as the density of the surface protrusions and to achieve high electro-magnetic conversion characteristics and good running performance with high compatibility.